The present invention generally relates to brush seals for rotary machines, such as steam and gas turbines, and, more particularly, is concerned with an arrangement and method for radially positioning a turbine brush seal.
Rotary machines, such as steam and gas turbines, used for power generation and mechanical drive applications are generally large machines having multiple turbine stages. In turbines, high pressure fluid flowing through the turbine stages must pass through a series of stationary and rotary components, and seals typically are used between the stationary and rotating components to minimize leakage of the fluid. The efficiency of the turbine is dependent on the ability of the seals to prevent fluid leakage.
Traditionally, one type of seal that is used to control fluid leakage in turbines is a labyrinth seal which has sharp rigid teeth. While the labyrinth seal has proven to be quite reliable, its performance degrades over time. This occurs as a result of transient events in which the stationary and rotating components move radially relative to and thus interfere with one another causing rubbing on the teeth of the labyrinth seal so as to enlarge the clearance between the stationary and rotating components and allow an increase of leakage.
Another type of seal that is used in combination with the labyrinth seal to improve leakage control is a brush seal. The brush seal is generally less prone to leakage than the labyrinth seal because the brush seal has seal bristles that can flex and thus better accommodate the relative radial movement between the stationary and rotating components. The brush seal also generally conforms better to surface non-uniformities than does the labyrinth seal. Such combination brush and labyrinth seal arrangements are disclosed in U.S. Pat. No. 5,749,584 to Skinner et al. assigned to General Electric Company, the assignee of the present invention, and U.K. Pat. Application No. 2,301,635 to Hemsley et al assigned to GEC Alsthom Limited.
A problem exists, however, with some combination brush and labyrinth seal arrangements. Accurate radial positioning of the brush seal relative to the rotor must be achieved in order to gain optimum performance while not adversely affecting rotordynamics. In the current method of assembly, a slot is provided in the labyrinth seal to receive the brush seal. The cross-sectional size of the slot is larger than the cross-sectional size of the portion of the brush seal that is received in the slot to facilitate the ease of mounting of the brush seal to the labyrinth seal. The larger cross-sectional size of the slot results in there being sufficient radial clearance between the brush seal and labyrinth seal to allow the brush seal to "float" radially within the slot, making it difficult to accurately align the brush seal to the rotor. The current method may allow the seal radial position to vary by several thousandths of an inch over its arc length. These variations may reduce the desired seal performance.
Consequently, a need exists for an innovation which will provide an effective solution to the aforementioned problem without introducing any new problems in place thereof.